Solar Technology Will Just Keep Getting Better: Here’s Why
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With the federal Investment Tax Credit phasing out, it’s a good time to take stock of the solar industry. both taking a look at where it has come from and where it is headed, especially in terms of innovation and evolving technology.
There are few individuals more qualified to discuss this topic than Jenya Meydbray, Founder and CEO of PVEL (PV Evolution Labs). His company – founded in 2010. performs independent qualification of photovoltaic solar equipment on behalf of large buyers and investors (PVEL tests both thin film and crystal silicon panels, but the vast majority of technology in the market is crystal silicon – which is where investors and developers are seeking the data).
A solar power plant is a capital-intensive venture, with an expected lifespan of as many as several decades. Operations and maintenance costs are relatively marginal, and the fuel is free, so the quality of the panels is perhaps the most critical element to consider in the overall equation.
As Medbray Комментарии и мнения владельцев, “Manufacturers are selling watts, while customers are making money off kWh and those are two different things.” This dynamic becomes increasingly important with assets that must perform over a large variety of conditions and lengthy timeframe. He asks rhetorically,
Have you ever seen a plastic kid’s toy left outside for a year? Polymers and plastics degrade in the field and solar panels are no different – they have polymers and plastics. We try and make it as simple as possible to provide comprehensive solutions through our qualification program.
PVEL evaluates panels by applying sophisticated reliability and performance-testing programs to ensure the panels will perform as promised and investors can feel confident ponying up their cash. It’s no small challenge, given that the cell and panel technology continues to evolve. And the industry has already come a long way since Meydbray started.
A look back at the past decade of innovation
Meydbray Комментарии и мнения владельцев that from an outsider’s perspective, a solar array “looks like a rectangle of crystalline solar cells glued to glass, bolted to a rack that goes through an inverter.” In that sense, he says, solar panels haven’t changed much in ten years and today they look more or less the same, “They still have 72 crystalline based cells glued to glass, bolted to a frame, and interconnected with an inverter.” However, he likens the cells to an engine in a car – an engine that has evolved greatly in the past decade, and whose costs have fallen dramatically, to perhaps 20% of what they were ten years ago.
Meydbray catalogs the items driving that trend in cost reductions, with one of the biggest levers being improved efficiencies in the manufacturing process itself. Take the utilization of silicon, for example. Although the price of silicon has plummeted from highs of 400 per kilogram to around 10/kg today, it’s still the most expensive input in a solar panel (for multi-silicon, an estimated 15-17% of total costs of goods sold). Thus, any ability to reduce the amount of silicon helps slash costs.
He cites the concept of ‘kerf loss,’ a term for the silicon lost in the sawing process during which raw silicon ingots are cut into cells. If silicon were wood, this would be the equivalent of sawdust that would go to waste. When a solar wafer – the precursor to the finished polished cell – is made – one essentially slices a giant log or brick of silicon into wafers. The widespread introduction of ultra thin diamond wire saws several years ago vastly reduces the amount of silicon lost in the process.
Meydbray observes that the cells thicknesses have stayed at about 180 microns for some time. Efforts to produce thinner cells resulted in frequent cracking during the production process, reducing overall yields. However, the widespread introduction of the diamond wire saw has recently allowed for the creation of thinner wafers (and therefore cells), though these haven’t yet moved into commercialization. He estimates the cost impact to be 1.5 cents/watt for every 10 microns of wafer thickness.
Then there is the conversion efficiency of the cell itself – how effectively it converts photons into a useful stream of electrons. This is important, since with higher efficiencies you get more watts out of the same rectangle of glass, the same frame, inverter, and labor. Since 2010, he notes, the absolute efficiency of the crystal silicon solar panel has gone up about.5% per year and “that’s pretty consistent. That’s huge. And it’s fundamental to continued cost reduction.”
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With PERC, Meydbray says, 23% cell efficiencies have been achieved, with average efficiencies at around 21.5% in the tens gigawatts of cells now being produced annually. He believes there is some efficiency runway left with PERC, but 23.5 % is probably the maximum that can be squeezed out. Meydbray also Комментарии и мнения владельцев that the distinction between mono and polysilicon cells is not as critical as it used to be. “Within these cell technologies, you can use multi or mono cells.” Mono cells used to couple higher efficiencies with higher costs, but “At this point, mono is becoming the same cost as multi, and in some cases is even cheaper,” he says.
Meydbray indicates the solar RD universe is now working on two technologies: heterojunction – which is a totally new cell technology (Meyer Burger is also working on this – which would necessitate a totally new greenfield solar manufacturing facility) and passivated contact “”which is incremental but difficult.” The jury is still out on both of these, but he Комментарии и мнения владельцев “we have a few years before we need to it to go up the efficiency curve.”
And then there’s bifacial
Meydbray indicates that once the PERC cells were created, it opened up an opportunity for bi-facial panels, which are just what they sound like; symmetrical solar panels that can harvest energy from each side. The original aluminum BSF solar panels were not symmetrical, but PERC is, “so when everybody moved to PERC they were essentially manufacturing bifacial solar cells. All you had to do was take off the back sheet and you had a bifacial panel.”
The manufacturing process for the industry giants like Jinko, Longi and others was “borderline trivial” he says, once they began making PERC cells. Clear back sheets had to be added and junction boxes (the enclosures on the module where all of the PV strings are connected that allows each module to be linked to the next) relocated to avoid blocking sunlight, but those were small obstacles.
As Meydbray explains it, the real challenge with bifacial is not in the manufacturing but in the implementation in the field, because a large number of new variables get added into the equation. To get best results from bifacial, one must maximize the amount of sunlight reflecting up to the downward facing panels. The panels must be high enough above the surface to allow maximum reflectivity, but the higher costs of steel racking affect the overall value proposition. One must also be careful to avoid having the frames block sunlight.
Placing panels higher off the ground, especially if they are on trackers that tilt the panels to follow the sun, also changes the potential wind loads to which the systems are exposed. In extreme cases, Meydbray Комментарии и мнения владельцев, “we have had wind-related failures from trackers. They can oscillate and blow apart.” steel can address that, but at an additional cost.
In addition, there is the issue of the mismatch between bifacial modules on edge of the system versus those in the middle that see less light on the backside. The modules are connected strings in parallel, feeding into a combiner box and inverter. Since they are in a series, they require the same current. Thus if the modules on the edge see more light than those in the middle, there is greater potential for mismatched losses.
Despite all of these various factors. and there are over a dozen to consider. Meydbray characterizes the ‘bifacial gain’ (the additional output compared with monfacial modules) as ranging from 5% to 20%,
it’s all about design conditions and cost optimization…bifacial will almost always beat monofacial economics – it’s the largest single step function improvement in levelized costs of electric since the introduction of trackers.
Meanwhile, other improvements are being made across the spectrum
The cells themselves have been increasing in size. What used to be a standard 156.75 millimeters (mm) cell was initially increased to 158 mm, and Meydbray indicates that cells are now moving to 161 mm. Longi. The world’s biggest monocrystalline silicon module maker, with plans to produce 30,000 MW of modules by 2021- recently announced a move to 166 mm, with plans to switch its entire production over by 2020.
The growth is relatively incremental, he says, “moving by one, two, three, or four millimeters…Somebody realized solar cell manufacturing equipment could fit a slightly larger cell” with the result that manufacturing costs fall on a per watt basis. When you get to 166 mm, though, it’s sufficiently bigger that you need incrementally different designs in the cell manufacturing equipment.
Agrivoltaics in Action
When Byron Kominek first approached officials in Boulder County, Colorado, about the idea of putting a photovoltaic display on his small family farm in 2018, he was surprised when they initially balked at his request. The county has aggressively pursued clean energy, and the city of Boulder has even committed to getting 100 percent of its electricity from renewable sources by 2030. Still, Kominek says, their “environmental conservation mindset” meant that “they were trying to conserve as much farmland and open space as they could, because they didn’t want everything to turn into strip malls.”
As progressive as they may have been, the officials saw the infrastructural requirements associated with solar power as incompatible with maintaining the integrity of agricultural spaces. But things changed once Boulder County analyzed its clean energy projections more closely. “They totaled up all the power that rooftop solar would produce and found that it wouldn’t even come close to providing all the power that the county consumes,” Kominek says.
After finally getting the green light to install solar, Kominek was busy trying to find the right balance between panels and plantings when he first heard about agrivoltaics from a friend of a friend who worked at the National Renewable Energy Laboratory in nearby Golden. He was immediately attracted to the idea. Now, three years later, Jack’s Solar Garden—named after Kominek’s grandfather, who first owned and worked the land—hosts more than 3,200 photovoltaic panels on about a sixth of the farm’s 24 acres, providing 1.2 megawatts of electricity, enough to power nearly 300 homes.
But even more impressive is what’s taking place under those panels. In the 2021 growing season, its first, Jack’s Solar Garden produced more than 8,600 pounds of organic vegetables, all of which grew beneath the cool, partially shaded “awning” of the photovoltaics. As of this writing, Kominek’s venture is the country’s largest commercially active agrivoltaics project. The solar garden functions in equal parts as a community farm, an education center, and a laboratory: a place where experiments can be conducted, effects can be observed, and the data can be recorded…right before being sautéed with a splash of garlic-infused olive oil and eagerly devoured. (Food grown under Kominek’s panels is harvested and distributed to the community by Sprout City Farms, a Denver-based nonprofit that promotes food system resilience and sustainable urban agriculture.)
Solar Is Blooming
Agrivoltaics, also referred to as “dual-use solar,” is already well known in a number of European and Asian countries, most notably Japan, where nearly 2,000 agrivoltaic installations currently generate more than 200 megawatts of electricity—enough to power more than 32,000 homes—and provide cover for more than 120 kinds of crops. In this densely populated country where agricultural land is relatively scarce, dual-use solar is expanding rapidly as farmers, clean energy advocates, and officials learn more about its benefits.
Here in the United States, agrivoltaics is also progressing, albeit more slowly. Ethan Winter, the Northeast solar specialist for the American Farmland Trust, which advocates for the protection of agricultural land and livelihoods through sustainable farming practices, is optimistic about dual-use solar’s prospects. “It has the potential to keep farmers farming, or even bring new farmers in,” he says, “and to stabilize a land base that might otherwise go to more permanent forms of development.”
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Winter adds that by tweaking the crops-under-panels formula a bit, landowners are also learning how they might benefit from other ecosystem services that agrivoltaics provides. Introducing pollinator-friendly plants, for example, can create habitat for beneficial insects such as bees and butterflies. Planting native vegetation can improve soil health by reducing erosion. “If done right, it could actually be a way to build soils,” Winter says. “There’s a regenerative angle that’s interesting.”
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Fascinatingly, research shows that the benefits of agrivoltaics cut both ways—that putting plants beneath solar panels can actually improve the performance of the panels, not just the plants. Because extreme heat negatively affects the efficiency of photovoltaic cells, they tend to generate more energy when the space around them is cooler. Placing abundant vegetation under panels leads to an increase in ground shade and humidity, which, in turn, leads to cooler photovoltaic cells and higher energy yields. One recent study found that panels with vegetation beneath them generated 10 percent more energy than those that had been placed over gravel.
Mind Your Ecosystem
Kominek and Winter are quick to point out that agrivoltaics isn’t a silver bullet. Its benefits, while real, are region- and plant-specific. It won’t work everywhere, with every kind of vegetation. “You have to be thinking about what you’re growing, and what the light requirements are,” says Winter. “Strawberries are different from corn, which is different from hay, which is different from kale.” And Kominek—whose experience inspired him to form a nonprofit dedicated to research and education around dual-use solar, the Colorado Agrivoltaic Learning Center—emphasizes that the climate of the given farmland is a big factor. “You probably won’t see the same things happening in Maine that you see in Tennessee, and you won’t see the same things happening in Tennessee that you see in New Mexico,” he says.
They also stress the need for incentives and market mechanisms geared toward farmers who want to pursue dual-use. Winter notes that the U.S. Departments of Energy and Agriculture have both recently made significant investments in agrivoltaics research, which he sees as a promising sign that some sort of large-scale federal aid may be on the way. Citing the many different Energy Department–sponsored loan programs, he imagines a set of criteria that—if met by landowners—would qualify them for preferential financing of dual-use projects, easing the significant up-front barriers to entry. “That would send a very clear signal to the private sector that we can lower our costs and capital.”
In the meantime, it may fall to small, independent farmers like Kominek to keep spreading the word and providing proof of concept. “I think it’s always better to try and do something more than just what’s standard—to try and do what’s better not just for my family but for the community,” he says. His farm is a shining example.
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Solar Cell Production: from silicon wafer to cell
In our earlier article about the production cycle of solar panels we provided a general outline of the standard procedure for making solar PV modules from the second most abundant mineral on earth – quartz.
In chemical terms, quartz consists of combined silicon-oxygen tetrahedra crystal structures of silicon dioxide (SiO2), the very raw material needed for making solar cells.
The production process from raw quartz to solar cells involves a range of steps, starting with the recovery and purification of silicon, followed by its slicing into utilizable disks – the silicon wafers – that are further processed into ready-to-assemble solar cells.
Only a few manufacturers control the whole value chain from quartz to solar cells. While most solar PV module companies are nothing more than assemblers of ready solar cells bought from various suppliers, some factories have at least however their own solar cell production line in which the raw material in form of silicon wafers is further processed and refined.
In this article, we will explain the detailed process of making a solar cell from a silicon wafer.
Solar Cell production industry structure
In the PV industry, the production chain from quartz to solar cells usually involves 3 major types of companies focusing on all or only parts of the value chain:
1.) Producers of solar cells from quartz, which are companies that basically control the whole value chain.
2.) Producers of silicon wafers from quartz – companies that master the production chain up to the slicing of silicon wafers and then sell these wafers to factories with their own solar cell production equipment.
3.) Producers of solar cells from silicon wafers, which basically refers to the limited quantity of solar PV module manufacturers with their own wafer-to-cell production equipment to control the quality and price of the solar cells.
For the purpose of this article, we will look at 3.) which is the production of quality solar cells from silicon wafers.
How are silicon wafers made?
Before even making a silicon wafer, pure silicon is needed which needs to be recovered by reduction and purification of the impure silicon dioxide in quartz.
In this first step, crushed quartz is put in a special furnace, and then a carbon electrode is applied to generate a high-temperature electric arc between the electrode and the silicon dioxide.
That process, called carbon arc welding (CAW), reduces the oxygen from the silicon dioxide and produces carbon dioxide at the electrode and molten silicon.
This molten silicon is 99% pure which is still insufficient to be used for processing into a solar cell, so further purification is undertaken by applying the floating zone technique (FTZ).
During the FTZ, the 99% pure silicon is repeatedly passed in the same direction through a heated tube. This process pushes the 1% impure parts to one end, with the remaining 100% pure parts remaining on the other side. The impure part can then be easily cut off.
Crystal seeds of silicon are in the so-called Czochralski (CZ) process put into polycrystalline silicon melt of the Czochralski growth apparatus. By extracting the seeds from the melt with the puller, they rotate and form a pure cylindrical silicon ingot cast out from the melt and which is used to make mono-crystalline silicon cells.
In order to make multi-crystalline silicon cells, various methods exist:
1.) heat exchange method (HEM)2.) electro-magneto casting (EMC)3.) directional solidification system (DSS)
DSS is the most common method, spearheaded by machinery from renowned equipment manufacturer GT Advanced. By this method, the silicon is passed through the DSS ingot growth furnace and processed into pure quadratic silicon blocks.
During the casting of the ingots, the silicon is often already pre-doped before slicing and selling the wafer disks to the manufacturers. Doping is basically the process of adding impurities into the crystalline silicon wafer to make it electrically conductive.
These positive (p-type) and negative (n-type) doping materials are mostly boron, which has 3 electrons (3-valent) and is used for p-type doping, and phosphorous, which has 5 electrons (5-valent) and is used for n-type doping. Silicon wafers are often pre-doped with boron.
Once we have our ingots ready, they can then – depending on the geometrical shape requirements, for solar cells usually space-saving hexagonal or rectangular shapes- be sliced into usually 125mm or 156mm silicon wafers by using a multiwire saw.
Processing of silicon wafers into solar cells
The standard process flow of producing solar cells from silicon wafers comprises 9 steps from a first quality check of the silicon wafers to the final testing of the ready solar cell.
Step 1: Pre-check and Pretreatment
The raw silicon wafer disks first undergo a pre-check during which they are inspected on their geometric shape and thickness conformity and on damages such as cracks, breakages, scratches, or other anomalities.
Following this pre-check, the wafers are split and cleaned with industrial soaps to remove any metal residues, liquids or other production remains from the surface that would otherwise impact the efficiency of that wafer.
Light reflection difference between a non-textured flat silicon wafer surface and a silicon wafer surface with a random pyramid texture
Step 2: Texturing
Following the initial pre-check, the front surface of the silicon wafers is textured to reduce reflection losses of the incident light.
For monocrystalline silicon wafers, the most common technique is random pyramid texturing which involves the coverage of the surface with aligned upward-pointing pyramid structures.
This is achieved by etching and pointing upwards from the front surface. The proper alignment of the pyramids etched out is a result of the regular, neat atomic structure of monocrystalline silicon.
The regular, neat atomic structure of monocrystalline silicon also benefits the flow of electrons through the cell as with fewer boundaries electrons flow much better. Therefore, monocrystalline silicon has an electrochemical structural advantage offering more efficiency over the grainy atomic structures of multi-crystalline silicon.
Now, with such a pyramid structure in place, the incident light does not reflect back and gets lost in the surrounding air but bounces back onto the surface.
Another, less common texturing technique is the inverted pyramid texturing. Instead of pointing upwards from the front surface, the pyramids are etched into the wafer’s surface, similarly achieving reflection losses of incident light trapped in the inverted pyramid holes.
The texturing of multi-crystallin silicon wafers requires photolithography – a technique involving the engraving of a geometric shape on a substrate by using light – or mechanical cutting of the surface by laser or special saws.
Step 3: Acid Cleaning
After texturing, the wafers undergo acidic rinsing (or: acid cleaning). In this step, any post-texturing particle remains are removed from the surface.
Using hydrogen fluoride (HF) vapor, oxidized silicon layers on the substrate can be etched away from the wafer surface. The result is a wet surface that can be easily dried.
By using hydrogen chloride (HCl), metallic residues on the surface can be absorbed by the chloride and thus removed from the wafer.
Step 4: Diffusion
Diffusion is basically the process of adding a dopant to the silicon wafer to make it more electrically conductive. There are basically 2 methods of diffusion: solid-state diffusion and emitter diffusion.
While the former method basically involves the already mentioned uniform doping of the wafers with the p-type and n-type materials, the emitter diffusion refers to the placing of a thin dopant material-containing coating on the wafer bypassing the wafers through a diffusion coating furnace.
Wafers that have already been pre-doped with p-type boron during the casting process are during the diffusion process given a negative (n-type) surface by diffusing them with a phosphorous source at a high temperature, creating the positive-negative (p-n) junction.
Why diffuse the wafers though? This junction of electron deficiency in the p-type and high electron concentration in the n-type allows for excess electrons from the n-type to pass to the p-type, a flow creating an electron field at the junction.
Step 5: Etching Edge Isolation
During diffusion, the n-type phosphorous diffuses not only into the desired wafer surface but also around the edges of the wafer as well as on the backside, creating an electrical path between the front and backside and in this way also preventing electrical isolation between the two sides.
The Latest Advancements in Solar Technology
With continuous and growing interest in the applications and benefits of solar technology, the industry has been in a constant state of innovation over the past several years. This innovation has led to advancements in solar efficiency, solar energy storage, printable solar technology, solar design technology, and more.
“Going solar” is more convenient than ever before because programs like Community Solar support local solar energy generation, and because the technologies that make this possible have seen many advancements in recent years. While most of the United States’ energy grid still comes from fossil fuel energy sources (e.g., natural gas, coal, and petroleum), solar power becomes more and more accessible whenever solar technologies evolve and become more efficient.
Clearway Community Solar is committed to achieving a clean energy future by making solar accessible to more homeowners, and believes that the more reliable and competitive solar options become, the closer we will get to achieving that goal. Our community solar programs have come a long way over the years, now servicing 28 states with the capacity to power about 2.7 million homes. And we won’t stop there!
Let’s take a look at some of the latest advancements in solar technology that are paving the way forward for a brighter, cleaner future.
Solar Efficiency
The efficiency of solar cells has accelerated at a remarkable pace over the last decade. Solar efficiency is measured by the amount of sunlight (irradiation) that falls on the surface of a solar panel and is available for energy conversion. With the latest advances in photovoltaic technology, the average conversion efficiency has increased from 15% to over 20%.
One factor that can lead to a loss of efficiency is the change in sun angle throughout the day as Earth rotates on its axis. Solar tracking systems. designed to tilt and position the panels towards the sun, first came around in the late 80s, but the technology had a long way to go. Today, a sun-tracking solar panel system with a single axis can see performance gains ranging from 25%-35%.
Solar Storage
Another limiting factor of solar energy has been the fact that the sun’s light does not shine on solar panels at night, so for those hours of darkness, energy could not be converted. In May 2016, Enel Green Power North America created a solar power plant that could produce electricity at night by storing energy collected from the sun during the day into a battery system.
Nighttime solar took a further leap when Stanford University researchers created solar panels that can generate electricity at night through a thermoelectric generator. Research conducted this year confirms that these nighttime cells produced enough energy to power a cellphone.
New Materials
The latest breakthrough in materials could move solar cell technology away from the current limitations of using silicon. In 2016, researchers made the first solar cell with perovskite crystals, which can be up to 20% more efficient than silicon-based solar cells. However, silicon still outperformed perovskite-based cells in terms of viability for commercial use. In June 2022, researchers at Princeton University developed the first commercially-viable perovskite solar cells. which can be manufactured at room temperature and require less energy to produce than silicon-based solar cells. The cheaper production cost and improved sustainability applied to a utility scale with a 30-year life expectancy is exciting news for the solar energy industry. Perovskite cells are also more flexible and can be transparent, which expands the realm of possibilities for their application and usefulness.
There have also been interesting and exciting breakthroughs in solar design, such as printable solar cells. which are flexible, lightweight, and can be placed on a wide range of other materials. These solar cells can even be printed in smaller sizes and incorporated into electronic accessories such as phones, tablets, and laptops.
This year, the world saw the first ever production-ready solar-powered car. While electric cars have been around for quite a while, this is the first vehicle in production where solar panels have been added to recharge the car’s battery while it drives, adding about 44 miles per day to the already 388 miles the car ranges between battery charges.